Traffic backs up on eastbound Interstate 70 during the morning rush hour in Denver, Jan. 9, 2017.

David Zabulowski/AP

The state Senate may have landed on a compromise to one of the thorniest issues at the legislature this year: how to pay for fixing Colorado roads.

From the opening day of this session, Senate Republicans have made it clear how they think the state should be funding its maintenance backlog. Senate Bill 001 would ask voters to authorize the sale of a massive bond package and commit a sizable chunk of state revenues in future years to paying it off.

But in a rare evening vote Wednesday, two Republicans broke with their party to support an amendment that re-writes SB18-001 and delays the bond ask to 2019. What do they get in return? The amendment commits a half a billion dollars in surplus tax revenue next year to new road projects.

Backers of the amendment want to keep the bond package off the 2018 ballot to clear the way for a business-backed proposal to raise the sales tax to fund transportation. They fear having two competing visions for how to fund transportation on the ballot would make it more likely voters reject both ideas.

Democratic state Sen. Rachel Zenzinger of Arvada helped broker the deal.

"I am very grateful to the two members of the Republican caucus who stood with us," she said after the vote. "That allows any other out-of-the building initiative that plans on moving forward a fair opportunity."

Republicans Don Coram of Montrose and Owen Hill of Colorado Springs were the ones who bucked their party to get the amendment passed.

"The voters will make the decision whether they want to do this,” Coram said. “It's just my job to give them the opportunity."

The amended bill faces a final vote in the Senate before heading to the House. It may face opposition there; some Democrats back a third funding option: asking voters for a gas tax increase, instead of selling bonds or raising sales taxes.

Earlier: Republicans Want Roads, Bridges Fixed And Expanded With No Other Detours